In the field of graphic arts, in order to obtain good reproduction of a halftone image in continuous gradation or good reproduction of a line work, a system of showing ultrahigh contrast (particularly, having .gamma. of 10 or more) photographic properties is necessary. An image formation system capable of obtaining ultrahigh contrast photographic properties by the development with a processing solution having good storage stability has been demanded and to cope with this demand, as described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781, a system of forming an ultrahigh contrast negative image having a .gamma. value exceeding 10 has been proposed, where a surface latent image type silver halide photographic light-sensitive material having added thereto a specific acylhydrazine compound is processed with a developer containing 0.15 mol/l or more of a sulfurous acid preservative and having a pH of from 11.0 to 12.3. This new system is characterized in that silver iodobromide or silver chloroiodobromide can be used, though only silver chlorobromide having a high silver chloride content can be used in conventional ultrahigh image-formation systems. Further, the new system is characterized in that a large amount of sulfurous acid preservative can be contained and relatively good storage stability is achieved, though conventional lith developers allow use of a very small amount of sulfurous acid preservative. However, developers having a pH of 11 or more are prone to air oxidation and unstable and cannot endure use or storage over a long period of time. A design for developing a silver halide light-sensitive material containing a hydrazine compound with a developer having a lower pH and forming a high contrast image is being attempted. JP-A-1-179939 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-1-179940 describe a method of using a light-sensitive material containing a nucleation development accelerator having an adsorptive group to a silver halide emulsion grain and a nucleating agent having the same adsorptive group, with a developer at a pH of 11.0 or less. However, the emulsion used in these inventions is a silver bromide or silver chlorobromide emulsion and fails to reach a satisfactory level in view of stability because the photographic properties greatly change along the progress of development or due to fluctuation in the composition of the processing solution.
U.S. Pat. Nos. 4,998,604, 4,994,365 and 4,975,354 disclose a hydrazine compound having a repeating unit of ethylene oxide or a hydrazine compound having a pyridinium group. However, seeing from the description in the Examples of these patents, the high contrast level is not satisfactory and it is difficult to achieve high contrast and necessary Dmax under practical development processing conditions. Further, the nucleation high contrast light-sensitive material using a hydrazine derivative is large in the variation width of the photographic properties ascribable to the change in the pH of the developer. The pH of the developer greatly changes, for example, by the increase due to air oxidation of the developer or thickening of the developer resulting from evaporation of water or by the decrease due to absorption of carbon dioxide in air. Accordingly, a design to reduce the dependency of the photographic properties on the pH of the developer is being attempted.
A dot-to-dot working light-sensitive material which is generally handled in a bright room predominates in the field of light-sensitive materials for photomechanical process. In this field, the reprinted letter is required to have high quality such that lean Chinese letters can be reproduced. Accordingly, development of nucleating agents having higher activity is being demanded. In particular, the bright room light-sensitive materials having sensitivity sufficiently low to allow handling even in a bright room are difficult of giving high contrast by the nucleating agent and therefore, development of nucleating agents having yet higher activity is being demanded.
To achieve these objects, for example, highly active hydrazine-base nucleating agents disclosed in JP-A-6-148828, JP-A-6-180477 and JP-A-6-194774 have been developed.
The nucleating agent having as an acyl group a substituted alkyl group substituted by at least one electron withdrawing group is particularly excellent because extremely high contrast photographic property can be obtained even with a developer having a pH of 11 or less and also changes in the photographic capability due to fatigue of the developer is small. However, in some cases, the nucleating agent itself is readily oxidized and the storability is in need of much improvement.
As the nucleating agent having an adsorption accelerating group, highly active hydrazine-base nucleating agents disclosed in JP-A-63-234244, JP-A-63-234245, JP-A-6-148828, JP-A-6-180477 and JP-A-6-194774 are already known, however, the nucleating agent itself is readily oxidized and many compounds need be improved in view of the storability. Further, yet higher activity is required for obtaining desired dot quality.
On the other hand, a method of obtaining a direct positive image by surface developing an internal latent image-type silver halide photographic emulsion in the presence of a nucleating agent and a photographic emulsion or light-sensitive material for use in the method are known, for example, in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552 and 3,317,322, British Patents 1,011,062, 1,151,363, 1,269,640 and 2,011,391, JP-B-43-19405 (the term "JP-B" as used herein means an "examined Japanese patent publication|"), JP-B-49-38164, JP-A-53-16623, JP-A-53-137133, JP-A-54-37732, JP-A-54-40629, JP-A-54-74536, JP-A-54-74729, JP-A-55-52055 and JP-A-55-90940.
In the above-described method for obtaining a direct positive image, a nucleating agent may be added to the developer, however, a method of adding the nucleating agent to a photographic emulsion layer or other appropriate layer of a light-sensitive material is more commonly used.
As the nucleating agent added to a direct positive silver halide light-sensitive material, hydrazine compounds are most well known and specific examples thereof include those described in Research Disclosure, No. 23510 (November, 1953), ibid., No. 15162, Vol. 151 (November, 1976), ibid., No. 17626, Vol. 176 (December, 1978). In general, the hydrazine-base nucleating agent provides large difference between the maximum density (Dmax) and the minimum density (Dmin) and is most excellent in the point of discrimination, however, it is deficient in that a high pH (11 or more) is required in the processing and improvement in this point has been demanded.